Construction of stabilised platform

ABSTRACT

The platform is mounted for tilting about longitudinal and transverse axes, and a level sensor operates, through an actuator control, to effect operation of an actuator to continually maintain the platform in a horizontally stabilized position. The actuator is further mounted on a vertically extending variable height actuator which, through a motion sensor, maintains the platform at a constant height in space despite movement of the floor of the vehicle on which the platform may be mounted. Thereby a patient riding in an ambulance and lying on the platform is prevented from being subjected to various vibrations resulting from motion of the vehicle.

United States Patent 191 Stirling et al. C

m- 3,s40,265 [451 Oct. 8, 1974 CONSTRUCTION OF STABILISED PLATFORM [75]Inventors: John Mowat Miller Stirling, Swords;

John Francis Colgan, Leixlip, both of Ireland I [73] Assignee: Institutefor Industrial Research and Standards, Dublin, Ireland [22 Filed: Sept.13, 1972 211 Appl. No.: 288,560 j [30] Foreign Application Priority DataSept. 13, 197'! Ireland 1157/71" 52 us. or. 296/19, 280/6 H, 5/62, I a m248/371 [51] Int. B60g17/04 [58] Field of Search 296/19; 5/62; 248/37l,.

[56] References Cited vroma on PATENTS 0R APPLICATIONS 859,952 l/l'96l.GreatBrita in 4296/19.

7 Primary Examiner-Philip Goodman Attorney, Agent, or Firm-McGlew andTuttle [5 7] ABSTRACT The platform is mounted for tilting aboutlongitudinal and transverse axes, and a level sensor operates, throughan actuator control, to effect operation of an actuator to continuallymaintain the platform in a horizontally stabilized position. Theactuator is further mounted on a vertically extending variable height actuator which, through a motion sensor, maintains the v platform at aconstant height in space despite movement of the floor of the vehicle onwhich theplatform may be mounted. Thereby a patient riding in an arnbulance and lying on the platform is prevented from being subjected tovarious vibrations resulting 1 from motionfof the vehicle. a

v 3 Claims, l3 Drawing Figures PATENTEDBBT w I '3'.e40.265

sum 10F e PATENTED 8 4 sum 3 or 6 CONSTRUCTION OF STABILISED PLATFORMFIELD AND BACKGROUND OF THE. INVENTION The present invention relates toa construction of stabilized platform for use invehicles and inparticular for use in ambulances.

When considering the problem of human vibration the body can for allpractical purposes be treated as a number of coupled spring-mass-dampersystems. It will be appreciated that the body has a number of internalorgans capable of movement relative to the body. When all these internalorgans are taken into account,

the overall mechanical system becomes extremely complex. Any vibrationof this complex structure ofinternal organs in the body will result inthe movement of organs and parts of the body with relation to each otherwhich will depend on the frequency and amplitude of oscillation.

It is not possible to predict with any accuracy the effects of vibrationon a body because of the variation of body measurements and structuresand the great number of possible modes of vibration to which the bodymay be subjected. Further the physiological reaction of peoplevariesenormously and is conditioned by other environmental influences. Such asfor example, the noise level, the temperature, the humidity and otherfactors. In the case of injured patients, there is the additionalcomplication in that the injuriesor body damage may be aggrevated bymechanical shock or vibrations and that pain may well be intensified.Obviously, the tolerance level to vibration of a subject with fracturedbones will be less than the tolerance of a completely healthy person.

The most commonly experienced symptom of vibration is that of motionsickness due to low frequencies and large amplitude, for example, inaircraft and ships.

It has been established that motion sickness can be induced inpractically any person if the vibration level is of sufficient intensityand duration. The symptoms can be described as a sudden onset of malaiseand nausea,

cold sweating and feeling of great dejection and apathy.

Vomiting often brings temporary relief. In the case of a healthyindividual. the symptom rapidly vanishes when the vibration ceases, butin the case of an unof the body to tolerate vibration is dependent notonly on the frequency and amplitude of vibration but on the duration ofexposure to such vibration. It will be appreciated therefore thatinjured or sick subjects would be even more susceptible to vibration.When attempting to define the vibration level which would be tolerableto a wide range of injured or disabled patients it is necessary to startby defining the tolerance level of healthy subjects.

It must be recognised however that there will always be a few patientsso badly injured that any vibration level or mechanical movement will beintolerable. On the other hand, any improvement on the type of vibrationcurrently experienced in an ambulance ride and in particular a highspeed ambulance ride, would be an advantage to the majority of ambulanceusers.

A supine patient will experience vertical vibration as well aslongitudinal and transverse vibration in a moving ambulance. It has beenfound that the main region in which stabilisation is required is forvertical vibrations of frequencies less than 2 Hz. where vibrationcontrol using mechanical components is particularly difficult. Thevibrations are transmitted to the patient through a chain of mechanicalelements comprising: the road surface to a tire, the tire through thewheel through the springs/damper to the chassis; the chassis to thestretcher base to thestretcher; and from the stretcher to the patient.All of these cascaded elements are capable of filtering or attenuatingthe effect of vibration but they are unfortunately also capableofamplifying the vibrations transmitted to the patient.

The main transverse forces acting upon a stretcher patient are due tothe centrifugal forces which appear during cornering. The durationdepends solely on the curvature of the road and on the speed-of theambulance. The acceleration and deceleration effects during normalstopping and starting in city traffic also impose head to foot forces onthe patient which are of the same low frequency nature as the transverseaccelerations.

It isnot possible to compensate for these two types of lateral forces inthe same way as for vertical acceleration, on account of the very largeamplitudes involved. Is is however possible to alleviate the worsteffects of these lateral acceleration forces by ensuring that they allact downwards at right angles to the body. The body is always subjectedto the downward force of gravity and a small increase in the apparentweight of the body gives rise to little additional discomfort. Theplatform on which the stretcher is placed can be tilted so thatthelateral force appears to act in combination with the normal weightvertically downwards'Colbeck [Physiological Responses to AccelerationColbeck B. R. Internal Report Jan. 1969] has computed the values ofangle tilt for various levels of steady lateral acceleration and alsothe percentage increases in weight to be experienced by the subject. Hisresults are summarised in the table.

, Lateral acceleration g 0.03

Angle 0mm 043 Increase in body wt. 0.5

mm su' 1 P20 1947 4024 so30' In an ambulance the peak acceleration is ofthe order of 0.25 g.

It will be appreciated that when a vehicle is carrying equipment,materials or other cargo susceptible to vibration that the provision ofa stabilized platform is very desirable.

' SUMMARY OF THEINVENTION The present invention is directed towardsproviding an improved construction of stabilized platform for vehicles.Accordingly the invention provides a stablised platform for mounting ina vehicle comprising: a base platform; pivot means for supporting thebase platform so to allow the base platform to tilt about a longitudinalaxis and a horizontal axis; means for controlling the tilt of baseplatform in response to lateral forces; a vertical variable heightactuator for support of the base platform in a vehicle; a motion sensoroperatively connected between the height actuator and the floor of thevehicle; and means for causing the height actuator to raise and lowerthe base platform-in opposition to the motion of the floor.

BRIEF DESCRIPTION OF TI-IE. DRAWINGS FIG. 2 is a further diagrammaticside view of a Stablised ambulance platform according to the invention,

FIG. 3 is a cross-sectionalview of a typical double acting force balancepneumatic cylinder used in some embodiments of the invention,

FIG. 4 is a diagrammatic side .view of a further stablized ambulanceplatform according to the present invention,

FIG. Sis an end view of a stablized ambulance platform illustrated inFiG. 4,

FIG. 6 is a view illustrating the forces acting on the stablizedambulance platform illustrated in FIGS. 4 and 5,

FIG. 7 is a diagrammatic side view of a still further stablizedambulance platform according to the invention,

FIG. 8 is a perspective view of another stablized ambulance platformmounted in an ambulance,

FIG. 9 is a side view of the stablized ambulance platform of FIG. 8.

FIG. is an end view of the stablized platform of FIG. 8,

FIG. 11 is a plan view of the stablized ambulance platform of FIG. 8,

FIG. 12 is a typical longitudinal cross-sectional view of portion of thestablized ambulance platform illustrated in FIG. 8 and FIG. 13 is atypical transverse cross-sectional view of portion of the ambulanceplatform illustrated in FIG. 8.

Referring to the drawings and initially to FIGS. 1 and 2 thereof, thereis illustrated a stabilized platform for mounting in a vehicle, in thiscase a stabilized ambulance platform. For clarity and to illustrate theprinciples of the invention this FIG. 1 illustrates the compensation oflateral forces only while FIG. 2 illustrates the compensation ofvertical forces or vibration. Referring to FIG. 1 the stabilizedambulance platform comprises a base platform 1 mounted on pivot means 2.The pivot means 2 are adapted to tilt the base platform about alongitudinal axis and a horizontal axis. An actuator 3 is connectedbetween the base platform 1 and the floor 4 of an ambulance. Theactuator 3 is adapted to tilt the base platform 1 in the direction ofthe arrow, that is to say about a transverse axis through the pivotmeans 2. The actuator 3 is connected to an actuator control 5 which isin turn operatively connected to a level sensor 6 above the baseplatform 1. A similar actuator, actuator control, and level sensor isprovided to control the tilting of the phase platform 1 about thelongitudinal axis. In operation, when the base platform 1 experiences alateral acceleration the actuator control 5 feeds a signal to theactuator 3 and causes the base platform 1 to tilt.

When the level sensor 6 is in an unbalanced condition due to lateralforces, a signal is fed to the actuator control 5. which in turn movesthe actuator 3 to tilt the base platform 1. When the base platform 1 andthe level sensor 6 are in balance the actuator control 5 is stopped. Ifthe level sensor 6 is a pendulum, balance is achieved when the pendulumacts at right angles to the base platform 1. Referring to FIG. 2 thebase platform 1 is mounted by means of a vertical variable heightactuator 7 on the floor 4. A motion sensor, for example, an inertialtransducer 8 is mounted between the base platform 1 and. the floor 4.The displacement of any floor movement is detected by the motion sensorand a signal fed to the actuator 7 in order to drive the actuator 7 inopposition to the motion of the floor 4 so that a patient remainsvirtually vibration free. A displacement transducer 9 stabilises theactuator 7 by fixing a mean suspension height. Referring to FIG. 3 thereis illustrated a double acting force balanced pneumatic cylinderindicated generally by the reference numeral 10. This is one typicalconstruction of a double acting force balanced pneumatic cylinder. Thereare, however, many such cylinders in commercial use. The force balancedpneumatic cylinder 10 comprises a positioner 11 and a pneumatic cylinder12 and piston 13. The positioner 11 has a control signalport l5, outletports 16 and 17, an inlet port 18 and an exhaust port 19. The outletports 17 and 18 are connected to the pneumatic cylinder 13. A piston 20and diaphragm 21 are mounted in the positioner 11 and are connected bymeans of a rod 22 to a piston 23 controlled by a compression spring 24.The compression spring 24 provides a feed back signal force to thepositioner. The compression of the compression spring 24 and hence thefeedback signal force is controlled by a pivotally mounted lever 25. Thepivotally mounted lever 25 is connected in known manner by a follower 26and a cam 27 on the piston rod of the cylinder 13 to the. prime mover itis desired to control. A valve stem 28 is mounted between the exhaustoutlet ports 16 and 17. The'double acting force balanced pneumaticcylinder 10 operates in conventional manner. An increase in the controlsignal pressure into the control signal port 13 causes the combinedassembly namely the piston 20, the rod 22 and the piston 23 to move tothe left under the increased pressure which. is acting against thepiston 20 and the diaphragm 21. The resulting position of the valve stem28 causes air to flow through the port 16 from the supply port 18 to thepneumatic cylinder 13 changing the piston 12 position. The compressionspring 24 is further compressed. When the condition is reached wherebythe force from the compression spring 24 equals the force of the controlpressure on the piston 20 and diaphragm 21 the movement of the rod 22will stop and the new position relative to control signal now exists. Adecrease in the pressure of control signal into the control port 13 willcause the valve stem 28 to move to the right, increase the pressure onthe right hand side of the piston 20 and diaphragm 21 and hence decreasethe pressure on the left hand side of the piston 20 and diaphragm 21thereby causing the piston rod 22 to move to the left thus causing adecrease in the compression of the compression spring 24 with the resultthat the control force and feed back force again equalise and furthermovement of the piston rod 22 is prevented.

If the positioner 11 is supplied with air underconstant pressure thenany movement of the positioner 11 relative to the cylinder will causethe piston 12 to move in the opposite direction. Referring to FIGS. 4, 5and 6 there is illustrated means for controlling the tilt of the baseplatform 1 about its longitudinal axis. A pendulum 30 is mounted beneatha base platform 1 and rigidly connected thereto. The base platform 1 isadapted for pivoting about a longitudinal axis in the direction of thearrow B as illustrated in FIGS. 4, 5 and 6. This stabilised platform isfor simplicity shown only pivoting about this one axis. In operation theforces on the pendulum are illustrated in FIG. 6. The forces acting bnthe pendulum are the weight W of the pendulum and the centrifugal forceF. These forces may be resolved into a resultant force R in conventionalmanner by a simple triangle of forces. Needless to say the base platform1 may be adapted to pivot about a transverse axis as well.

The pendulum 30 may be connected by a universal joint to the vehicle andconnected rigidly by transversely and longitudinally disposed links tothe base platform 1. Many arrangements of this will readily come to mindto those skilled in the art. Dampers may be incorporated to adjust theresponse of the base platform 1 to the movement of the pendulum 30.

Referring to FIG. 7 there is illustrated in partially diagrammatic forma variable height actuator which comprises a support bellows 40, aninlet valve 41 controlled by an electro magnet 42 and an outlet valve 43con-' trolled by an electro magnet 44. The support bellows 40 supportsthe base platform 1 and a displacement transducer 45 is connectedbetween the base platform 1 and the floor 4 of the vehicle. Thedisplacement transducer 45 is fed through a conventional delay 46 to acomparator 47. Also fed through the comparator'47 is a mean pressurecontrol signal from an electrical height control 48. The signal from thecomparator 47 is fed to valve control circuits 49 which control inconventional manner the operation of the electro magnets 42 and 44. Apressure transducer 50 is operatively connected between the supportbellows 40 and the comparator 47. In this embodiment of the inventionany motion of the floor 4 relative to the base platform 1 causes achange in internal air pressure in the bellows 40 and is measureddirectly by the pressure transducer 50 which feeds a signal through tothe comparator 47. This causes the comparator 47 to comparethe signalbeing delivered by the displacement transducer with that of the heightcontrol 48. The signal is then sent to the valve control circuits 49 andeither the inlet valve 41 or the outlet valve 43 is opened, thus causingthe pressure in the support bellows 40 to be increased or decreased,thus raising or lowering the base platform 1 relative to the floor 4.The patient lying on the base platform 1 does not therefore experiencethe motion of the floor. Under very slow changes in internal pressurethe reaction'of pressure transducer 50 may not be adequate. Thedisplacement transducer 45 and the delay 46 act to stabilise the systemand prevent large movements or creep of the base platform 1. Needless tosay the arrangements previously described for the compensation oflateral forces may be incorporated in this embodiment and previouslywould be. However, for clarity they have been omitted. I

Referring to FIGS. 8 to 13 there is illustrated an alternativeembodiment of the invention which is a stabilised platform for mountingin a vehicle and in particular a stabilised platform for mounting in anambulance,

having a floor 60 and a wall 61. The stabilized platform comprises abase platform 62, pivotably mounted at 63, within a frame 64 which is inturn pivotably mounted at 65 within a frame 66. It will be appreciatedthat the base platform 62 is capable of tilting about a longitudinalaxis and transverse axis, that is to say the axes defined by thesupports at 63 and 65. Compensation for v lateral forces may be achievedas hereinbefore described, and they are omitted from the drawings forclarity. The frame 66 issupported by means of a pair of cantileveredarms 67. The. cantilivered arms are mounted by means of rollers 68 onbars 69, rigidly mounted between support members 70 and 71 on the wall61. A double acting force balanced pneumatic cylinder 72 is mounted onthe wall 61 by a support plate I 73. The double acting force balancedpneumatic cylinder 72 supports on its piston rod 74 a pulley 75. Alength of flexible wire 76 is connected between the sup port member 71and the frame 66. It will be appreciated that vertical movement of thepiston rod 74 will cause vertical movement of the frame 66.

The double acting force balanced pneumatic cylinder 72 is fed andoperated as described with reference to FIG. 3. In operation the baseplatform 62 in response to lateral forces may be tilted, while thedouble acting force balanced pneumatic cylinder 72 will raise andlowerthe base platform 62 in the opposite direction to any motion imparted tothe floor 60 by the vehicle travelling over the road.

We claim:

1. A stabilised platform for mounting in a vehicle comprising: a baseplatform; pivot means supporting the base platform so as to allow thebase platform to tilt about a longitudinal axis and a horizontal axis;means controlling the tilt of the base platform in response to lateralforces; a vertical variable height actuator supporting the base platformin a vehicle and comprising a double acting force-balanced pneumaticcylinder; a motion sensor operatively connected between the heightactuator and the floor of the vehicle; and means causing the heightactuator to raise or lower the base platform in opposition to the motionof the floor.

2. A stabilized platform as claimed in claim 1 in which the meanscontrolling the tilt of the base platform about each axis comprises atilt actuator;

a level sensor;

and control means operatively connected between the tilt actuator andthe level sensor whereby the resultant forces of gravity and lateralforces acts downwards at right angles to the base platform.

3. A stabilised platform as claimed in claim 2 in which the controlmeans controlling the tilt of the base cylinder.

force balances pneumatic

1. A stabilised platform for mounting in a vehicle comprising: a baseplatform; pivot means supporting the base platform so as to allow thebase platform to tilt about a longitudinal axis and a horizontal axis;means controlling the tilt of the base platform in response to lateralforces; a vertical variable height actuator supporting the base platformin a vehicle and comprising a double acting force-balanced pneumaticcylinder; a motion sensor operatively connected between the heightactuator and the floor of the vehicle; and means causing the heightactuator to raise or lower the base platform in opposition to the motionof the floor.
 2. A stabilized platform as claimed in claim 1 in whichthe means controlling the tilt of the base platform about each axiscomprises a tilt actuator; a level sensor; and control means operativelyconnected between the tilt actuator and the level sensor whereby theresultant forces of gravity and lateral forces acts downwards at rightangles to the base platform.
 3. A stabilised platform as claimed inclaim 2 in which the control means controlling the tilt of the baseplatform about each axis comprises a double acting force balancespneumatic cylinder.